1. Field of the Invention
The present invention belongs to a technical field of image display. In particular, the present invention relates to a display image quality measuring system capable of easily evaluating the image quality of a display by a commercial image pickup device of a conventional type such as a digital camera without using a measuring device such as a microdensitometer.
2. Description of the Related Art
A diagnostic image taken by a medical measurement apparatus such as an MRI diagnostic apparatus, an X-ray diagnostic apparatus, or an FCR (Fuji computed radiography) is generally recorded in a translucent image recording film such as an X-ray film, a film photosensitive material, or the like, and reproduced as a translucent image. The film in which the diagnostic image is reproduced is set in a lighting system which is called Schaukasten and observed with a state in which the film is irradiated with light from its rear side so that a diagnosis is conducted.
In contrast to this, in recent years, a diagnostic image taken by a medical measurement apparatus is displayed on a display such as a CRT (cathode ray tube) or an LCD (liquid crystal display device) and observed to conduct a diagnosis (electronic Schaukasten).
When a diagnosis is conducted using an image reproduced in a film, the image is, so to speak, a fixed one. Although there is a certain difference resulting from luminance of Schaukasten and an observation environment, the same image is basically observed so that a diagnosis can be conducted.
However, when a diagnosis using a display image (hereinafter referred to as a display diagnosis) is conducted, what is fixed is image data, and a displayed image, that is, a diagnostic image varies according to the kind, the state, the change over time, or the like of the display. Such a variation in image raises a serious problem in which wrong diagnosis may be caused. Therefore, when the display diagnosis is conducted, the quality control (QC) of a display is important to keep the state of the display appropriate.
For example, when a deterioration of luminance is caused in a CRT by a change over time, or the like, an output of electron beam is enhanced to restore luminance. Now, according to such a luminance correction method, the luminance is restored. However, the beam size of the electron beam becomes larger according to the enhancement of the output. As a result, the sharpness of an image is reduced.
In a conventional method, whether the sharpness of a display is appropriate or not is determined by visual observation. However, according to such a method, the sharpness cannot be evaluated quantitatively.
On the one hand, when the sharpness of a display is quantitatively evaluated, for example, there is required a measurement method of photographing a displayed image in a film and measuring the image by a microdensitometer with respect to its sharpness, which consumes time and uses technical equipment. It is extremely difficult to conduct the quality control of the display for which such measurement is required in the location where a display is used, such as a hospital.
An object of the present invention is to solve the above problems of the prior art, and therefore to provide a display image quality measuring system capable of easily and quantitatively measuring the image quality of a display for displaying such images as a medical image for diagnosis using a commercial image pickup device of a conventional type such as a digital camera without using a dedicated technical device for measurement such as a microdensitometer which is expensive.
In order to attain the object described above, the present invention provides a display image quality measuring system comprising:
image pickup means for conducting photographing which includes a two dimensional solid state sensor and an imaging optical system, with a photographing condition in which a gradation characteristic is not saturated, a gradation characteristic under the photographing condition, and a dark level being known;
control means for instructing a display to display an adjustment pattern and a measurement pattern; and
analyzing means for analyzing photographing data obtained by the image pickup means,
wherein the display is instructed to display the adjustment pattern, the adjustment pattern thus displayed is photographed by the image pickup means, photographing data of the adjustment pattern is supplied to the analyzing means, and a measurement photographing condition is determined by the analyzing means using the photographing data, the photographing condition, the gradation characteristic, and the dark level, and
wherein the display is instructed to display the measurement pattern, the measurement pattern thus displayed is photographed by the image pickup means under the determined measurement photographing condition, photographing data of the measurement pattern is supplied to the analyzing means, and the photographing data of the measurement pattern is analyzed by the analyzing means.
Preferably, the photographing data is corrected using the dark level, and when the photographing data is color photographing data, the photographing data is converted into monochrome photographing data and then determination of the measurement photographing condition and analysis of the photographing data are conducted.
And, preferably, the image pickup means is a digital camera.
And, preferably, parameters in the photographing condition are an exposure time, a diaphragm value, and photographing sensitivity.
Further, preferably, when sharpness of the display is measured, the display is instructed to display as the measurement pattern solid images of two kinds of luminance and high frequency images in which straight lines of the two kinds of luminance extending in a direction orthogonal to a sharpness measurement direction are alternately arranged for every K pixels (K is an integer of 1 or higher) in the measurement direction, photographing data of the high frequency images are averaged in the direction orthogonal to the measurement direction to compute a first profile of each of the high frequency images in the measurement direction, moving average processing is conducted for the first profile of each of the high frequency images to compute a second profile of each of the high frequency images, and the sharpness of the display is measured using average values of relative maximum peaks and average values of relative minimum peaks in the second profiles obtained by the moving average processing and average values of the photographing data of the solid images.
And, preferably, the adjustment pattern and the measurement pattern are identical.
Further, preferably, when sharpness of the display is measured, in one or both of the adjustment pattern and the measurement pattern, a solid image of low luminance, a solid image of high luminance, a high frequency image in which a line of the high luminance and a line of the low luminance each extending in an H-direction are alternately arranged for every K pixels (K is an integer of 1 or higher) in a V-direction, and a high frequency image in which a line of the high luminance and a line of the low luminance each extending in the V-direction are alternately arranged for every K pixels (K is an integer of 1 or higher) in the H-direction are displayed on one screen, and the high frequency images are arranged in a central portion of a region to be photographed by the image pickup means, the solid images are arranged outside the central portion, and the respective images are arranged such that any of the images does not exist in a region of another image extended in the H-direction and the V-direction.